How important is Sophomore year in high school?

Up until the first semester of 10th grade, I had a GPA of 3.5, but this semester something went screwy and I started not doing much of my schoolwork at all for quite a few weeks. I don't know why, and I'm trying to get help from my parents to discipline me more... But I had A's and B's, and now I'm getting 40's and things in some of my classes. I'm an intelligent person, I just got lazy. I figure I'll want to go to at least culinary school and the community college. How important is this past semester if I want a good career?